Temperature controlled short duration ablation with multiple electrodes

ABSTRACT

Apparatus, including a catheter configured to be inserted into an organ of a human body. A plurality of electrodes are deployed on the catheter, the electrodes being configured to transfer radiofrequency (RF) ablation energy to tissue of the organ. The apparatus also includes a power supply configured to supply the RF ablation energy at a level of up to 100 W to each of the plurality of electrodes simultaneously, so as to ablate respective sections of the tissue of the organ in contact with the electrodes.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. Application No.15/994,459, filed May 31, 2018, which claims the benefit of U.S.Provisional Pat. Application 62/529,158, filed 6 Jul. 2017, both ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to surgery, and specifically to surgeryusing radiofrequency ablation.

BACKGROUND OF THE INVENTION

Radiofrequency (RF) ablation is a treatment modality that kills unwantedtissue by heat. Starting with cardiac arrhythmia treatment in the 1980s,RF ablation has found clinical application in a number of diseases, andis now the treatment of choice for certain types of cardiac arrhythmia,and certain cancers. During RF ablation, an electrode is inserted intoproximity with the target region under medical imaging guidance. Tissuesurrounding the electrode in the target region is destroyed by heatingvia RF electric current.

U.S. Pat. Application 2003/0236455 to Swanson et al., describes a probeassembly for mapping and ablating pulmonary vein tissue. The probeassembly includes an expandable and collapsible basket assembly havingmultiple splines. One or more of the splines carry one or moreelectrodes adapted to sense electrical activity in the pulmonary veintissue.

U.S. Pat. Application 2014/0066921 to Coe et al., describes ballooncatheter neuromodulation systems. The application refers to modulating(e.g., disrupting, ablating, stimulating) the nerves by mechanicalcompression, energy delivery, or fluid delivery.

U.S. Pat. 5,931,835 to Mackey, describes a radio frequency energydelivery system for multipolar electrode catheters. It is stated thatthe power, voltage, or temperature delivered to multiple electrodes maybe dynamically controlled.

EP Patent Application 1,645,234 to Buysse et al., describes anelectrosurgical system employing multiple electrodes. The system employsmultiple electrodes for producing large ablation volumes in tissue.

U.S. Pat. Application 2002/0161361 to Sherman et al., describes an RFablation system using electrodes and having automatic temperaturecontrol. It is stated that a select number of the electrodes have atemperature sensing device associated with them for providing atemperature signal indicative of the temperature at the interfacebetween the electrode and tissue.

U.S. Pat. Application 2001/0020166 to Daly et al., describes a systemfor simultaneous unipolar multi-electrode ablation. The system is statedto ablate tissue using unipolar RF energy simultaneously delivered tomultiple electrodes.

U.S. Pat. 6,319,249 to Töllner, describes an ablation catheter with,inter alia, a plurality of ablation electrodes, at least one energysource, and switching elements for connecting the electrodes to theenergy source.

U.S. Pat. Application 2008/0161797 to Wang et al., describes ablationcatheter electrodes having multiple thermal sensors. The electrodes arestated to contain two or more thermal sensors at different positionswithin the electrode.

Documents incorporated by reference in the present patent applicationare to be considered an integral part of the application except that, tothe extent that any terms are defined in these incorporated documents ina manner that conflicts with definitions made explicitly or implicitlyin the present specification, only the definitions in the presentspecification should be considered.

SUMMARY OF THE DISCLOSURE

An embodiment of the present invention provides apparatus, including:

-   a catheter configured to be inserted into an organ of a human body;-   a plurality of electrodes deployed on the catheter, the electrodes    being configured to transfer radiofrequency (RF) ablation energy to    tissue of the organ; and-   a power supply configured to supply the RF ablation energy at a    level of up to 100 W to each of the plurality of electrodes    simultaneously, so as to ablate respective sections of the tissue of    the organ in contact with the electrodes.

In a disclosed embodiment the plurality of electrodes includes up totwelve electrodes, and the power supply is configured to provide up to1.2 kW of radiofrequency power.

In a further disclosed embodiment the apparatus includes a plurality oftemperature sensors each coupled to measure a respective temperature ofone of the plurality of electrodes, and the power supply is configured,when the respective temperature of the one of the plurality ofelectrodes in contact with one of the sections of tissue exceeds aselected maximum temperature, to reduce the level of power of the RFablation energy supplied to the one of the plurality of electrodes.

In a yet further disclosed embodiment the apparatus includes a processorwhich is coupled to the power supply and which is configured tosimultaneously measure a respective impedance to the RF ablation energyfor each of the plurality of electrodes, and, when a change in theimpedance to one of the plurality of electrodes in contact with one ofthe sections of tissue exceeds a preset value, to halt supply of the RFablation energy from the power supply to the one of the plurality ofelectrodes.

The catheter may include a balloon catheter. Alternatively, the cathetermay include a basket catheter.

There is further provided, according to an embodiment of the presentinvention, apparatus, including:

-   a catheter configured to be inserted into an organ of a human body;-   a first electrode and a second electrode deployed on the catheter,    the electrodes being configured to transfer radiofrequency (RF)    ablation energy to tissue of the organ;-   a first temperature sensor coupled to measure a first temperature of    the first electrode;-   a second temperature sensor coupled to measure a second temperature    of the second electrode;-   a power supply configured to provide the RF ablation energy;-   a switch connected to the power supply and configured to direct the    RF ablation energy to one of the first and second electrodes; and-   a processor configured, while the power supply is providing the RF    ablation energy via the switch to the first electrode, to monitor    the first and second temperatures and, responsively to the monitored    temperatures, to toggle the switch so as direct the RF ablation    energy to one of the first and second electrodes.

In an alternative embodiment the processor is configured, upon sensingthat the first temperature exceeds a predefined ablation temperaturethreshold while the second temperature does not exceed the ablationtemperature threshold, to toggle the switch so as to direct the RFablation energy to the second electrode.

In a further alternative embodiment the processor is configured tomonitor a first time for ablation via the first electrode and a secondtime for ablation via the second electrode, and, responsively to themonitored times, to toggle the switch so as direct the RF ablationenergy to one of the first and second electrodes. Typically, theprocessor is configured, upon sensing that the first time for ablationequals or exceeds a preset first time for ablation for the firstelectrode while the second time for ablation is less than a presetsecond time for ablation for the second electrode, to toggle the switchso as to direct the RF ablation energy to the second electrode.

In a yet further alternative embodiment the first electrode isconfigured to transfer the RF ablation energy at a first power level,and the second electrode is configured to transfer the RF ablationenergy at a second power level, and the power supply is configured tosupply power to the electrodes at a level no greater than a maximum ofthe first and second power levels.

The catheter may be a balloon catheter. Alternatively, the catheter maybe a basket catheter.

There is further provided, according to an embodiment of the presentinvention, a method, including:

-   inserting a catheter into an organ of a human body;-   deploying a plurality of electrodes on the catheter, the electrodes    being configured to transfer radiofrequency (RF) ablation energy to    tissue of the organ; and-   supplying with a power supply the RF ablation energy at a level of    up to 100 W to each of the plurality of electrodes simultaneously,    so as to ablate respective sections of the tissue of the organ in    contact with the electrodes.

There is further provided, according to an embodiment of the presentinvention, a method, including:

-   inserting a catheter into an organ of a human body;-   deploying a first electrode and a second electrode on the catheter,    the electrodes being configured to transfer radiofrequency (RF)    ablation energy to tissue of the organ;-   coupling a first temperature sensor to measure a first temperature    of the first electrode;-   coupling a second temperature sensor to measure a second temperature    of the second electrode;-   configuring a power supply to provide the RF ablation energy;-   connecting a switch to the power supply and configuring the switch    to direct the RF ablation energy to one of the first and second    electrodes; and-   while the power supply is providing the RF ablation energy via the    switch to the first electrode, monitoring the first and second    temperatures and, responsively to the monitored temperatures,    toggling the switch so as direct the RF ablation energy to one of    the first and second electrodes.

The present disclosure will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an invasive medical procedureusing apparatus, according to an embodiment of the present invention;

FIG. 2 is a schematic perspective view of a balloon catheter in itsinflated configuration, according to an embodiment of the presentinvention;

FIG. 3 is a schematic view of the balloon catheter deployed in apulmonary vein, according to an embodiment of the present invention;

FIG. 4 is a schematic view of a plurality of leaves of flexible circuitassemblies, according to an embodiment of the present invention;

FIG. 5 is a schematic perspective view of a flexible circuit assemblypartly lifted from the balloon catheter according to an embodiment ofthe present invention;

FIG. 6 is a block diagram of the apparatus of FIG. 1 , according to afirst embodiment of the present invention;

FIG. 7 is a flowchart of steps of an algorithm performed in operation ofthe first embodiment;

FIG. 8 is a block diagram of the apparatus of FIG. 1 , according to asecond embodiment of the present invention; and

FIG. 9 is a flowchart of steps of an algorithm performed in operation ofthe second embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS Overview

In embodiments of the present invention, a catheter, having a pluralityof electrodes deployed thereon, is inserted into an organ, typically theheart, of a human body. The electrodes are configured to transferradiofrequency (RF) ablation energy to tissue of the organ.

In a first embodiment of the invention, a power supply supplies the RFablation energy at a level of up to 100 W to each of the plurality ofelectrodes simultaneously, so as to ablate respective sections of thetissue of the organ in contact with the electrodes. During suchsimultaneous ablation, careful monitoring of the temperature andimpedance at each electrode separately allows embodiments of the presentinvention to perform multiple tissue ablations at the powers of up to100 W at each electrode without adverse effects on the tissue. The highpowers enable an overall ablation session for the multiple ablations tobe shortened to times typically of no more than 10s.

In a second embodiment of the invention, the plurality of electrodescomprise a first electrode and a second electrode. A first temperaturesensor measures a first temperature of the first electrode, and a secondtemperature sensor measures a second temperature of the secondelectrode. A power supply provides the RF ablation energy, and a switchis connected to the power supply and is configured to direct the RFablation energy to one of the first and second electrodes. A processoris configured, while the power supply is providing the RF ablationenergy via the switch to the first electrode, to monitor the first andsecond temperatures and, responsively to the monitored temperatures, totoggle the switch so as direct the RF ablation energy to one of thefirst and second electrodes. Switching the RF energy between theelectrodes, depending on the temperatures of the electrodes, ensuresefficient utilization of a power supply that may be unable to providehigh powers to both electrodes simultaneously, due to a maximum powerrating of the power supply.

Detailed Description

In the following description, like elements in the drawings areidentified by like numerals, and like elements are differentiated asnecessary by appending a letter to the identifying numeral.

FIG. 1 is a schematic illustration of an invasive medical procedureusing apparatus 12, according to an embodiment of the present invention.The procedure is performed by a medical professional 14, and, by way ofexample, the procedure in the description hereinbelow is assumed tocomprise ablation of a portion of a myocardium 16 of the heart of ahuman patient 18. However, it is understood that embodiments of thepresent invention are not merely applicable to this specific procedure,and may include substantially any procedure on biological tissue or onnon-biological materials.

In order to perform the ablation, medical professional 14 inserts aprobe 20 into a sheath 21 that has been pre-positioned in a lumen of thepatient. Sheath 21 is positioned so that a distal end 22 of probe 20enters the heart of the patient. A balloon catheter 24, which isdescribed in more detail below with reference to FIGS. 2 -5 , isdeployed through a lumen 23 of the probe 20, and exits from distal end22 of the probe 20.

As shown in FIG. 1 , apparatus 12 is controlled by a system processor46, which is located in an operating console 15 of the apparatus.Console 15 comprises controls 49 which are used by professional 14 tocommunicate with the processor. During the procedure, the processor 46typically tracks a location and an orientation of the distal end 22 ofthe probe 20, using any method known in the art. For example, processor46 may use a magnetic tracking method, wherein magnetic transmitters25X, 25Y and 25Z external to patient 18 generate signals in one or morecoils positioned in the distal end of the probe 20. The CARTO® systemavailable from Biosense Webster, of 33 Technology Drive, Irvine, CA92618, uses such a tracking method.

The software for the processor 46 may be downloaded to the processor inelectronic form, over a network, for example. Alternatively oradditionally, the software may be provided on non-transitory tangiblemedia, such as optical, magnetic, or electronic storage media. Thetracking of the distal end 22 is typically displayed on athree-dimensional representation 60 of the heart of patient 18 on ascreen 62.

In the description herein processor 46 is assumed to be formed from anysuitable integrated circuits, including, but not limited to, an ASIC(application specific integrated circuit), an FPGA (field-programmablegate array), an MCU (microcontroller unit), and a CPU.

In order to operate apparatus 12, the processor 46 communicates with amodule bank 50, which has a number of modules used by the processor tooperate the apparatus. Thus, the bank 50 comprises a temperature module52, a power supply 54, a switch 57, an irrigation module 55, and anelectrocardiograph (ECG) module 56, the functions of which are describedbelow. Bank 50 typically comprises other modules, such as a force modulefor measuring the force on the distal end 22, and a tracking module foroperating the tracking method used by the processor 46. For simplicity,such other modules are not illustrated in FIG. 1 . The modules maycomprise hardware as well as software elements.

FIG. 2 is a schematic perspective view of the balloon catheter 24 in itsinflated configuration, and FIG. 3 is a schematic view of the ballooncatheter deployed in a pulmonary vein, according to an embodiment of thepresent invention. In a disclosed embodiment, where the balloon catheter24 is used to ablate an ostium 11 of a lumen, such as a pulmonary vein13, as shown in FIG. 3 , the balloon catheter 24 is supported by atubular shaft 70 having a proximal shaft portion 82 and a distal shaftend 88. The shaft 70 comprises a hollow central tube 74, which permits asupport catheter to pass therethrough and through the distal shaft end88. The support catheter may be a focal linear catheter or a lassocatheter 72, as illustrated. The lasso catheter 72 may be inserted intothe pulmonary vein (PV) to position the balloon catheter 24 correctlywith respect to the ostium prior to ablation of the ostium. The distallasso portion of the catheter 72 is typically formed of shape-memoryretentive material such as nitinol.

It is understood that the balloon catheter 24 may also be supported by alinear or focal catheter 99 (as shown in broken lines in FIG. 2 ) in thePV or elsewhere in the heart. The focal catheter 99 may include a forcesensor at its distal tip. Suitable force sending distal tips aredisclosed in U.S. Pat. No. 8,357,152, issued on Jan. 22, 2013 to Govariet al., titled CATHETER WITH PRESSURE SENSING, and in U.S. Pat.Application 2011/0130648, to Beeckler et al., filed Nov. 30, 2009,titled CATHETER WITH PRESSURE MEASURING TIP, the entire contents of bothof which are incorporated herein by reference. Any catheter used inconjunction with the balloon catheter may have features and functions,including, for example, pressure sensing, ablation, diagnostic, e.g.,navigation and pacing.

An inflatable balloon 80 of the balloon catheter 24 has an exterior wallor membrane 26 of a bio-compatible material, for example, formed from aplastic such as polyethylene terephthalate (PET), polyurethane orPEBAX®. The shaft 70 and the distal shaft end 88 define a longitudinalaxis 78 of the balloon 80. The balloon 80 is deployed, in a collapseduninflated configuration, via the lumen 23 of the probe 20, and may beinflated after exiting from the distal end 22. The balloon 80 may beinflated and deflated by injection and expulsion of a fluid such assaline solution through the shaft 70. The membrane 26 of the balloon 80is formed with irrigation pores or apertures 27 (shown in FIG. 5 )through which the fluid can exit from the interior of the balloon 80 tooutside the balloon for cooling the tissue ablation site at the ostium.While FIG. 3 shows fluid exiting the balloon 80 as jet streams, it isunderstood that the fluid may exit the balloon with any desired flowrate and/or pressure, including a rate where the fluid is seeping out ofthe balloon.

The membrane 26 supports and carries a combined electrode andtemperature sensing member which is constructed as a multi-layerflexible circuit electrode assembly 84. The “flex circuit electrodeassembly” 84 may have many different geometric configurations. In theillustrated embodiment, the flex circuit electrode assembly 84 has aplurality of radiating leaves or strips 30.

FIG. 4 is a schematic view of a plurality of leaves 30, according to anembodiment of the present invention. The leaves 30 are evenlydistributed about the distal end 88 and the balloon 80. Each leaf haswider proximal portion that gradually tapers to a narrower distalportion. FIG. 4 shows, by way of example, ten radiating leaves 30, butit will be understood that embodiments of the present invention may havemore or fewer than ten leaves. In one embodiment, referred to below,there are twelve leaves 30.

With reference to FIGS. 2 and 4 , each leaf 30 has a proximal tail 31Pand a distal tail 31D. The proximal tail 31P is tucked under andfastened to the catheter 24 by a proximal ring 28P mounted on theproximal shaft portion 82 of the shaft 70. The distal tail 31D is tuckedunder and fastened to the catheter 24 by a distal ring (not shown).Either or both sets of tails 31D and 31P may be further covered by arespective semispherical cap, such as distal cap 28D. One or morecontact electrodes 33 on each leaf come into galvanic contract with theostium 11 during an ablation procedure, during which electrical currentflows from the contact electrodes 33 to the ostium 11, as shown in FIG.3 . In the description, electrodes 33 are differentiated as necessary byappending a letter to the identifying numeral, so that there areelectrodes 33A, 33B,

FIG. 5 is a schematic perspective view of a flexible circuit assemblypartly lifted from the balloon catheter according to an embodiment ofthe present invention. For simplicity, the flex circuit electrodeassembly 84 is described with respect to one of its leaves 30 as shownin FIG. 5 , although it is understood that the following description mayapply to each leaf of the assembly. The flex circuit electrode assembly84 includes a flexible and resilient sheet substrate 34, constructed ofa suitable bio-compatible materials, for example, polyimide. In someembodiments, the sheet substrate 34 has a greater heat resistance (or ahigher melting temperature) compared to that of the balloon membrane 26.In some embodiments, the substrate 34 is constructed of a thermosetmaterial having a decomposition temperature that is higher than themelting temperature of the balloon membrane 26 by approximately 100° C.or more.

The substrate 34 is formed with one or more irrigation pores orapertures 35 that are in alignment with the irrigation apertures 35 ofthe balloon member 26 so that fluid passing through the irrigationapertures 35 can pass to the ablation site on the ostium.

The substrate 34 has a first or outer surface 36 facing away from theballoon membrane 26, and a second or inner surface 37 facing the balloonmembrane 26. On its outer surface 36, the substrate 34 supports andcarries the contact electrodes 33 adapted for tissue contact with theostium. On its inner surface 37, the substrate 34 supports and carries awiring electrode 38. The contact electrode 33 delivers RF energy,supplied by power supply 54, to the ostium during ablation and isconnected to a thermocouple junction (described in more detail below)for temperature sensing of the ostium. In the illustrated embodiment,the contact electrode 33 has a longitudinally elongated portion 40 and aplurality of thin transversal linear portions or fingers 41 extendinggenerally perpendicularly from each lateral side of the elongatedportion 40 between enlarged proximal and distal ends 42P and 42D,generally evenly spaced therebetween. The elongated portion 40 has agreater width and each of the fingers has a generally uniform lesserwidth. Accordingly, the configuration or trace of the contact electrode33 resembles a “fishbone.”

Formed within the contact electrode 33 are one or more exclusion zone47, each surrounding an irrigation aperture 27 formed in the substrate26. The exclusion zones 47 are voids purposely formed in the contactelectrode 33, as explained in detail further below, so as to avoiddamage to the contact electrode 33 during construction of the electrodeassembly 84 in accommodating the irrigation apertures 27 at theirlocations and in their function.

Also formed in the contact electrode 33 are one or more conductive blindvias 48 which are conductive or metallic formations that extend throughthrough-holes in the substrate 34 and are configured as electricalconduits connecting the contact electrode 33 on the outer surface 36 andthe wiring electrode 38 on the inner surface 37. It is understood that“conductive” is used herein interchangeably with “metallic” in allrelevant instances.

Attached, e.g., by a solder weld 63, to an active solder pad portion 61Aof electrode 38 are a wire pair, e.g., a constantan wire 51 and a copperwire 53. The copper wire 53 provides a lead wire to the wiring electrode33, and the copper wire 53 and the constantan wire 51 provide athermocouple whose junction is at solder weld 63, so that weld 63 isalso referred to herein as thermocouple junction 63. Junction 63 acts astemperature sensor, and is also referred to herein as sensor 63, and thesensors are differentiated as necessary by appending a letter to theidentifying numeral, so that there are sensors 63A, 63B, .... Thus, foreach electrode 33A, 33B, ..., there is a respective temperature sensor63A, 63B, ....

The wire pair 51/53 is passed through a through-hole 29 formed in themembrane 26. It is understood that, in other embodiments in the absenceof the through-hole 29, the wire pair 51/53 may run between the membrane26 and the substrate 34 and further proximally between the membrane 26and the proximal tail 31P until the wire pair 51/53 enters the tubularshaft 70 via another through-hole (not shown) formed in the tubularshaft sidewall closer to the proximal ring 28.

The flex circuit electrode assembly 84, including the leaves 30 and thetails 31P and 31D, is affixed to the balloon membrane 26 such that theouter surface 36 of the substrate 34 is exposed and the inner surface 37of the substrate 34 is affixed to the balloon membrane 26, with thewiring electrode 38 and wire pair 51/53 sandwiched between the substrate34 and the balloon membrane 26.

First Embodiment

FIG. 6 is a block diagram of apparatus 12, according to a firstembodiment of the present invention. In FIG. 6 processor 46, temperaturemodule 52, power supply 54, switch 57, and catheter 24 are illustratedas rectangular blocks, and the block diagram also illustrates sensingsignals, control signals, and power connections between the differentelements of apparatus 12. Switch 57 comprises a plurality ofsub-switches 59A, ..., 59D, ..., 59N, collectively termed sub-switches59. Catheter 24 comprises electrodes 33A, ..., 33D, ... 33N, which arerespectively attached to sensors 63A, ..., 63D, ... 63N, and which arealso connected to receive power from the power supply via sub-switches59A, ..., 59D, ..., 59N. In the first embodiment of apparatus 12illustrated by FIG. 6 , all sub-switches 59 are constantly closed, sothat, when activated, power supply 54 supplies power simultaneously toall electrodes 33.

Thus, in operation of apparatus 12, and referring also to FIG. 1 ,temperature module 52 receives sensing signals from each sensor 63 ofeach electrode 33, and uses the signals to determine a tissuetemperature, which is the temperature of the tissue surface in contactwith each of the electrodes. The temperature module is configured tocalculate the tissue temperature at a fixed rate, herein assumed to beevery 33 ms, but other embodiments may calculate the tissue temperatureat higher or lower rates. The temperature module passes the calculatedtissue temperature values for each of electrodes 33 to processor 46,which in turn passes control signals to power supply 54.

Power supply 54 provides RF power, separately and individually, viarespective sub-switches 59, to each electrode 33 of balloon catheter 24.In some embodiments the RF power is provided via copper wire 53.Alternatively or additionally, the RF power may be provided to therespective electrodes 33 by another conductor. The power for eachelectrode may be supplied in a range of 1W to 100 W, and the power maybe provided simultaneously to all electrodes 33. Thus, in an embodimentof the invention comprising twelve electrodes 33, module 54 may supply100 W to each electrode, for an overall power input to the catheter of1.2 kW.

In order to supply these high powers, it will be understood that leadsto electrodes 33, and substrate 34, provide sufficient insulation so asto avoid any arcing from the electrodes.

In embodiments of the present invention the power supply can beconfigured to provide a maximum RF power to each electrode 33 that canbe set within a range of 70 W -100 W. In some embodiments, the modulecan be configured to provide a further RF power to each electrode 33 ina different range from the maximum. In one embodiment the further powerrange is 20 W - 60 W, and the further power is typically provided afterthe maximum power. The maximum RF power and the further RF power arealso termed herein the first power and the second power.

The power supply also measures an impedance of each electrode 33. Theimpedance is measured at a predefined rate, herein assumed to be every500 ms, but other embodiments may measure the impedance at a lower orhigher rate.

For each electrode 33, the maximum power for the electrode, and the timeperiod for which the power is delivered, is selected by professional 14.The professional may also select values of the power less than 70 W, andcorresponding time periods for delivery of this reduced power. Theactual power delivered by any given electrode is determined by thetissue temperature received from temperature module 52 for thatelectrode, as described below.

Typically, during an ablation session, the impedance presented to agiven electrode 33 decreases. Embodiments of the present invention alsocheck if the impedance presented to each electrode increases from aprevious impedance measurement by more than a pre-set value, hereinassumed to be 7Q, although other embodiments may use larger or smallervalues of impedance for the pre-set value. An increase of impedancetypically occurs if there is an unwanted change in the tissue beingablated, such as charring or steam popping. If, for any given electrode33, the impedance increases by more than the pre-set value, the powersupply is configured to stop the RF delivery to the given electrode.

Notwithstanding the powers selected by the professional, the powersupply is configured to reduce the power delivered by a given electrode,typically by between approximately 5% and approximately 95%, if thetissue temperature for the given electrode, received from thetemperature module, reaches or exceeds a predefined temperaturethreshold. The predefined temperature threshold is a maximum allowabletemperature that is set by professional 14, and in the followingdescription the predefined temperature threshold is also referred to asthe maximum allowable temperature.

In one embodiment, power for a given electrode that has been originallyset to 90 W is reduced to 50 W after 4 s, regardless of the reading fromsensor 63. In an embodiment of the present invention, the maximumallowable temperature for all electrodes may be set within a range 60°C. - 65° C. Typically, exceeding the maximum allowable temperaturecauses undesirable effects such as charring, coagulation on an electrode33, and/or steam pops in the tissue being ablated.

Irrigation module 58 (FIG. 1 ) governs the rate at which irrigationfluid is delivered to balloon catheter 24. In embodiments of the presentinvention it may be set within the range of 5 - 60 ml/min.

FIG. 7 is a flowchart of steps of an algorithm performed in operation ofthe first embodiment of apparatus 12. The steps of the flowchart assumethat the block diagram of FIG. 6 applies, i.e., that all sub-switches 59are constantly closed, so that power supply supplies powersimultaneously to all electrodes 33.

In a range setting step 200, ranges for each of the variable parametersreferred to above are set. The ranges may be set individually for eachelectrode 33. While in one embodiment this is typically the same for allelectrodes, this is not necessarily the case, and in other embodimentsranges are different for different electrodes.

In one embodiment the ranges are set as shown in Table I. Typically, forthe powers, an operator of apparatus 12, usually professional 14, onlysets the first power, while the second power is automatically pre-set byprocessor 46.

TABLE I Parameter Range Maximum Power Delivered (First Power) 50 W - 100W Second Power 15 W - 50 W Maximum allowable temperature 50° C. - 65° C.Irrigation rate 5 - 60 ml/min First Time Period (during which FirstTarget Power is operative) 1 s to 6 s Second Time Period (during whichSecond Target Power is operative) Up to 14 s Overall Time Period forPower Delivery (Sum of First and Second Time Periods) 1 s - 20 s

Range setting step 200 is implemented before professional 14 performs anablation.

At the beginning of an ablation session, in a probe introduction step202, professional 14 inserts balloon catheter 24 into a desired locationin myocardium 16, using the tracking system incorporated into apparatus12.

In a select value step 204, prior to performing the ablation procedure,professional 14 selects values of the parameters listed in Table I thatare to be used in the procedure, and uses controls 49 to provide thevalues to the system. Alternatively, the professional selects apredetermined set of the values of the parameters listed in Table I,typically by choosing a “recipe” comprising the values, from a group ofsuch recipes. The selected values typically depend on the depth oflesion it is desired to form by the procedure. For lesions of 1 - 3 mmdepth the inventors have found that the values of the parameters givenby Table II give good results. For lesions of 4 - 5 mm depth theinventors have found that the values of the parameters given by TableIII give good results.

It will be understood that the selections made by professional 14 instep 204 are for each electrode 33 individually. Thus for twelveelectrodes 33, twelve sets of parameters are selected. While theselections may be the same for all electrodes 33, this is not arequirement. For example, the professional may select parametersaccording to Table II for some electrodes, and according to Table IIIfor other electrodes.

In addition, while the selected parameters for each electrode 33 aretypically applied simultaneously to all the electrodes, this is also nota requirement. Thus the parameters may be provided at least partiallysequentially, and/or in a staggered fashion, e.g., 2 s after ablationhas been started for one electrode, ablation may be started for aneighboring electrode.

TABLE II Lesions of 1 - 3 mm Depth Parameter Value First Target Power 90W Second Target Power Not set Maximum allowable temperature 60° C.Irrigation rate 8 ml/min Time Period 4 s

TABLE III Lesions of 4 - 5 mm Depth Parameter Value First Target Power90 W Second Target Power 50 W Maximum allowable temperature 60° C.Irrigation rate 8 ml/min First Time Period 4 s Second Time Period 6 s

Those having skill in the art will be able to determine, for otherlesion depths, required values of the parameters within the ranges givenby Table I, without undue experimentation.

In a begin RF delivery step 206, professional 14 operates apparatus 12,with the parameter values selected in step 204, in order to perform theablations of electrodes 33. Typically, during the ablations, screen 62displays values of the parameters listed in Table I to the professional.Screen 62 may also be configured to display to the professional, bymethods which are known in the art, the progress of the RF deliveries tothe individual electrodes. The display of the progress may be graphical,such as a simulation of the dimensions of the respective lesions as theyare produced by the ablations, and/or alphanumeric.

During the RF delivery procedure processor 46 uses the temperaturemodule and the power supply to perform a number of checks on theprogress of the procedure, as shown in the flowchart by decision steps208, 210, and 214.

Processor 46 operates steps 208 - 222 of the algorithm for each givenelectrode 33 individually and separately, measuring the impedance forthe given electrode and the tissue temperature provided by sensor 63 ofthe electrode. For clarity, in the description below the ablations ofall electrodes are assumed to be implemented simultaneously, in whichcase the processor performs steps 206 - 222 simultaneously for all thedifferent electrodes. Those having skill in the art will be able toadapt the description, mutatis mutandis, for cases of non-simultaneousablation.

In step 208, processor 46 uses power supply 54 to check if the impedanceof a given electrode 33 has increased by more than the pre-set impedancevalue. If it has, the system halts the procedure for the given electrodein a termination step 216. If step 208 returns a negative value, controlof the algorithm continues to decision step 210.

In step 210, the processor uses temperature module 52 to check if themeasured tissue temperature for the given electrode, as measured bysensor 63 of the electrode, exceeds or reaches the predefinedtemperature threshold, i.e., the maximum allowable temperature selectedin step 204. If decision step 210 returns a positive value, the powersupply, in a reduction step 218, reduces the power to the givenelectrode.

The power reduction in step 218 is a function of a number of parameters:

-   A difference in temperature between the maximum allowable    temperature T (set in step 204) and the measured temperature T_(t)    at a time t,-   A change of measured temperatures between sequential temperature    measurements, i.e., T_(t-1) - T_(t),-   A target power P, where if the flowchart is functioning in the first    time period, P is the first target power, and if the flowchart is    functioning in the second time period, P is the second target power,    and-   A power P_(t) measured at time t.

In one embodiment the following equations applies for the powerreduction:

$\text{Δ}\text{P}( \text{T} ) = \frac{\text{a}( {\text{T}_{\text{t} - 1} - \text{T}_{\text{t}}} )}{\text{T}} + \frac{\text{b}( {\text{T} - \text{T}_{\text{t}}} )}{\text{T}}$

where ΔP (T) is a fractional change in power as a function oftemperature, and a and b are numerical constants. In a disclosedembodiment a = 10 and b = 1.

$\text{Δ}\text{P}( \text{p} ) = \frac{( {\text{P} - \text{P}_{\text{t}}} )}{\text{P}}$

where ΔP (p) is a fractional change in power as a function of power.

ΔP = min (ΔP(T), ΔP(p))

where min (ΔP (T) , ΔP (p) ) is the minimum of ΔP (T) and ΔP (p), and ΔPis the fractional change in power applied in step 218.

Typically, power reduction step 218 is performed reiteratively withdecision step 210, until the measured temperature is below thepredefined temperature threshold.

If step 210 returns a negative value, control continues to decision step214.

In decision step 214, processor 46 checks if the time for the ablationby the given electrode, set in step 204, has been reached. If it has,then the flowchart ends. If the time has not been reached, controlpasses to a continuing ablation step 222, where the processor continuesthe ablation by the given electrode, and returns to decision steps 208,210, and 214. Decision steps 208, 210, and 214 have been presentedsequentially in the flowchart for simplicity and clarity. Typically,however, the system uses the power supply to perform the steps inparallel.

Second Embodiment

FIG. 8 is a block diagram of apparatus 12, according to a secondembodiment of the present invention. Apart from the differencesdescribed below, the block diagram for the second embodiment isgenerally similar to that of the first embodiment (FIG. 6 ) and elementsindicated by the same reference numerals in both block diagrams arecommon. In contrast to the first embodiment, in the second embodiment ofapparatus 12 illustrated by FIG. 6 , all sub-switches 59 are notconstantly closed. Rather, as described in more detail below, duringoperation of apparatus 12 at any given instant some sub-switches 59 areopen and some are closed. FIG. 8 illustrates, as an example,sub-switches 59A and 59N being open, while sub-switch 59D is closed.FIG. 9 is a flowchart of steps of an algorithm performed in operation ofthe second embodiment of apparatus 12.

In contrast to the first embodiment described above, wherein powersupply 54 is able to simultaneously supply ablation power to allelectrodes 33, in the second embodiment described hereinbelow the powersupply module is limited to being only able to supply ablation powersimultaneously to a subset, i.e., a reduced number, of electrodes 33,due to a maximum power rating of the power supply.

In an initial step 250, professional 14 inserts balloon catheter 24 intoa desired location in myocardium 16, using the tracking systemincorporated into apparatus 12.

In an assignment step 254, the professional assigns ablation parametersindividually for each electrode 33, i.e., a power to be delivered byeach electrode, and a time duration for the delivery. While in somecases these may be the same for each electrode 33, e.g. 90 W for 4 s foreach electrode 33, there is no requirement that this is the case. Forexample, electrode 33A may be assigned 80 W for 3 s, electrode 33B maybe assigned 60 W for 4 s, electrode 33C may be assigned 70 W for 3 s,and so on.

In some embodiments the assignment may be determined by the positioningof catheter 24 (as implemented in step 250) with respect to tissue beingablated. E.g., if balloon catheter 24 has been positioned to contactostium 11 of pulmonary vein 13 (FIG. 3 ), the power and the time may beset according to a measured or assumed thickness of the ostium sectioncontacting respective electrodes 33.

In addition to assigning ablation parameters individually for eachelectrode, in step 254 a predefined temperature threshold, for thetemperature measured by sensors 63, is assigned. The predefinedtemperature threshold may be assigned by professional 14, oralternatively may be preset for apparatus 12. The temperature thresholdis, as stated above with reference to the first embodiment, a maximumallowable temperature for a given electrode 33. As is also stated above,if the temperature of tissue becomes greater than the temperaturethreshold, the tissue may suffer undesired effects.

In an initial ablation step 258, the professional activates apparatus 12to begin ablation. On activation, processor 46 divides electrodes 33into two groups: a first group, herein termed active electrodes 33,which are to be used for ablation, and a second group, herein termedquiescent electrodes 33, which are not to be used for ablation.Processor 46 may make the selection by closing or opening sub-switches59. Thus, active electrodes 33 are selected by closing a first set ofsub-switches 59, so that there is a conducting line from power supply 54to the electrodes for these electrodes. Acquiescent electrodes 33 areselected by opening a second set of sub-switches 59, so that there is noconducting line from power supply 54 to the electrodes for theseelectrodes. The processor stores identities of active electrodes 33 inan active electrode register, and identities of quiescent electrodes 33in a quiescent electrode register.

Processor 46 divides the electrodes into the two groups so that thetotal power required to be delivered to the active group, as determinedaccording to the ablation parameters assigned in step 254, does notexceed a maximum power rating of power module 54. For example, if thereare twelve electrodes 33, each assigned in step 254 to deliver 50 W, andmodule 54 has a maximum power rating of 500 W, then the processor mayassign up to five electrodes to be in the active group, and theremainder, in this case seven or more, to be in the quiescent group.Typically, processor 46 assigns the active group to have the largestpossible number of electrodes 33, consistent with the constraint thatthe maximum power rating of power module 54 is not exceeded. In someembodiments, the assignment may initially be made on a random basis.Alternatively, professional 14 may provide an indication to theprocessor of how the assignment is to be made on a non-random basis, forexample, by providing the processor with a priority order of electrodes33 to be assigned to the active group.

In a continuation step 262, processor 46 begins ablation by activatingpower supply 54, so that the module supplies power to each of electrodes33 of the active group, i.e., to each of the electrodes havingrespective sub-switches 59 closed, according to the power levels set instep 254.

In a first decision step 264, processor 46 checks if a given activeelectrode 33 has completed its assigned ablation. For example, if inassignment step 254 a given electrode is assigned to ablate with a power50 W for 4 s, the processor checks if an aggregate time during which thegiven electrode is dissipating power of 50 W is equal to 4 s. If thefirst decision returns negative, then the processor proceeds to atemperature decision step 268, where the processor checks, using theappropriate sensor 63, if the given active electrode temperature exceedsthe temperature threshold set in step 254. If the threshold is notexceeded, i.e., the temperature condition returns negative, controlreturns to first decision step 264.

Thus, providing both first decision step 264 and temperature decisionstep 268 return negative, the processor iteratively loops through thesedecisions, and continues checking whether a given active electrode hascompleted its assigned ablation, and whether its temperature, asmeasured by its sensor, exceeds the temperature threshold.

Processor 46 simultaneously implements the iterative loop describedabove for all active electrodes. The iterative loop follows a returnline 270 of the flowchart.

For any given active electrode, the iteration stops if either firstdecision step 264 or temperature decision step 268 returns positive, asis explained in more detail below.

If temperature decision step 268 returns positive, i.e., if a sensor 63of an active electrode 33 being checked indicates that the thresholdtemperature has been exceeded, control transfers to a switch togglingstep 272. Thus, if decision 268 returns positive, the iterative loop forthe active electrode being checked is broken.

In switch toggling step 272 processor 46 performs the following actions:

-   Power to the active electrode checked prior to entry to step 272 is    terminated, by the processor toggling in switch 57 the sub-switch 59    supplying the active electrode from a closed state to an open state.-   Using electrode identities in the quiescent electrode register, the    processor selects a quiescent electrode to be converted to an active    electrode. The selection is consistent with the constraint that the    maximum power rating of power module 54, when the new active    electrode is operative, is not exceeded.-   The selected quiescent electrode is powered on, so becoming an    active electrode, by the processor toggling in switch 57 the    sub-switch 59 supplying the selected electrode from an open state to    a closed state.-   The processor updates the active electrode register and quiescent    electrode register accordingly. I.e., the identity of the electrode    checked in decision step 268 is transferred from the active    electrode register to the quiescent electrode register, and the    identity of the quiescent electrode selected in the switch toggling    step is transferred from the quiescent electrode register to the    active electrode register.

Once the processor has performed the actions described above for step272, control returns to decision step 264, so that the iterative loop ofdecision steps 264, 268, and line 270 restarts.

As stated above, the iterative loop may also terminate if decision step264 returns positive. In this case the electrode being checked hascompleted its ablation, and control continues to a record completedelectrodes step 276. In step 276 the processor transfers the identity ofthe electrode checked in decision step 264 from the active electroderegister to a completed ablation register.

The flowchart continues to a decision step 280, wherein the processorchecks the completed ablation register to see if all electrodes havecompleted their ablation. If step 280 returns negative, i.e., there isat least one electrode that has not completed its assigned ablation,control continues to switch toggling step 272, described above, whereinthe active electrode checked in condition 264 is switched off, and anavailable quiescent electrode is switched on.

If step 280 returns positive, i.e., all electrodes have completed theirablation, then the active electrode checked in decision step 264, whichis the last operative electrode, is switched off in a final flowchartstep 284, and the flowchart ends.

While the description above has used a balloon catheter to providemultiple electrodes 33 for respective ablations, it will be understoodthat embodiments of the present invention are not limited to ballooncatheters. Thus embodiments of the present invention comprise othercatheters, such as basket catheters, lasso catheters, and focalcatheters, with multiple electrodes that are used for respectiveablations.

It will thus be appreciated that the embodiments described above arecited by way of example, and that the present invention is not limitedto what has been particularly shown and described hereinabove. Rather,the scope of the present invention includes both combinations andsubcombinations of the various features described hereinabove, as wellas variations and modifications thereof which would occur to personsskilled in the art upon reading the foregoing description and which arenot disclosed in the prior art.

1. A system comprising: a power supply configured to supplyradiofrequency (RF) ablation energy to each of a plurality of electrodesdeployed on a catheter so as to ablate tissue of an organ in contactwith a respective one of the plurality of electrodes, each of theplurality of electrodes having a temperature sensor; a temperaturemodule configured to determine a temperature of the surface of the organtissue in contact with each of the plurality of electrodes in responseto receiving sensing signals from each electrode temperature sensor; oneor more processors coupled to the power supply and the temperaturemodule; a non-transitory computer readable medium storing a plurality ofinstructions, which when executed, cause the one or more processors to:i) receive a predefined power of RF ablation energy to be delivered byeach electrode, a predefined time duration for delivering the predefinedpower by each electrode and a predefined temperature threshold of thesurface of the tissue in contact with each electrode, ii) identify anactive group of the plurality of electrodes to be used for ablation andan inactive group of the plurality of electrodes, wherein a sum of thepre-determined power to be delivered by each active electrode does notexceed a maximum power of the power supply, iii) cause the power supplyto continue delivering power to each electrode in the active group ofelectrodes that has not delivered the predefined power for thepredefined time duration when the temperature of the tissue in contactwith the respective electrode does not exceed the temperature threshold,iv) cause each electrode in the active group of electrodes that has notdelivered the predefined power for the predefined time duration tobecome inactive when the temperature of the tissue in contact with therespective electrode exceeds the temperature threshold, v) identify, inresponse to an active electrode becoming inactive, an electrode in theinactive group of electrodes to become active such that sum of thepre-determined power to be delivered by each electrode in the activegroup of electrodes does not exceed the maximum power of the powersupply, and vi) cause each electrode in the active group of electrodesthat has delivered the predefined power for the predefined time durationto become inactive.
 2. The apparatus according to claim 1, wherein theplurality of electrodes comprises up to twelve electrodes, and whereinthe power supply is configured to provide up to 1.2 kW of radiofrequencypower.
 3. The apparatus according to claim 1, wherein the cathetercomprises a balloon catheter.
 4. The apparatus according to claim 1,wherein the catheter comprises a basket catheter.
 5. A method,comprising: receiving, by a processor coupled to a power supply and atemperature module, a predefined power of radiofrequency (RF) ablationenergy to be delivered by each of a plurality of electrodes deployed ona catheter, a predefined time duration for delivering the predefinedpower by each electrode and a predefined temperature threshold of asurface of organ tissue in contact with a respective one of theplurality of electrodes, the temperature module being configured todetermine a temperature of the tissue surface in in contact with each ofthe plurality of electrodes in response to receiving sensing signalsfrom temperature sensors in each respective electrode; identifying anactive group of the plurality of electrodes to be used for ablation andan inactive group of the plurality of electrodes, wherein a sum of thepre-determined power to be delivered by each active electrode does notexceed a maximum power of the power supply; causing the power supply tocontinue delivering power to each electrode in the active group ofelectrodes that has not delivered the predefined power for thepredefined time duration when the temperature of the tissue in contactwith the respective electrode does not exceed the temperature threshold;causing each electrode in the active group of electrodes that has notdelivered the predefined power for the predefined time duration tobecome inactive when the temperature of the tissue in contact with therespective electrode exceeds the temperature threshold; identifying, inresponse to an active electrode becoming inactive, an electrode in theinactive group of electrodes to become active such that sum of thepre-determined power to be delivered by each electrode in the activegroup of electrodes does not exceed the maximum power of the powersupply; and causing each electrode in the active group of electrodesthat has delivered the predefined power for the predefined time durationto become inactive.
 6. The method according to claim 5, wherein theplurality of electrodes comprises up to twelve electrodes, and whereinthe power supply is configured to provide up to 1.2 kW of radiofrequencypower.
 7. The method according to claim 5, wherein the cathetercomprises a balloon catheter.
 8. The method according to claim 5,wherein the catheter comprises a basket catheter.
 9. A computer programproduct, comprising a non-transitory computer-readable medium havingcomputer-readable program code embodied therein to be executed by one ormore processors coupled to a power supply and a temperature module, theprogram code including instructions to: receive a predefined power ofradiofrequency (RF) ablation energy to be delivered by each of aplurality of electrodes deployed on a catheter, a predefined timeduration for delivering the predefined power by each electrode and apredefined temperature threshold of a surface of organ tissue in contactwith a respective one of the plurality of electrodes, the temperaturemodule being configured to determine a temperature of the tissue surfacein in contact with each of the plurality of electrodes in response toreceiving sensing signals from temperature sensors in each respectiveelectrode; identify an active group of the plurality of electrodes to beused for ablation and an inactive group of the plurality of electrodes,wherein a sum of the pre-determined power to be delivered by each activeelectrode does not exceed a maximum power of the power supply; cause thepower supply to continue delivering power to each electrode in theactive group of electrodes that has not delivered the predefined powerfor the predefined time duration when the temperature of the tissue incontact with the respective electrode does not exceed the temperaturethreshold; cause each electrode in the active group of electrodes thathas not delivered the predefined power for the predefined time durationto become inactive when the temperature of the tissue in contact withthe respective electrode exceeds the temperature threshold; identify, inresponse to an active electrode becoming inactive, an electrode in theinactive group of electrodes to become active such that sum of thepre-determined power to be delivered by each electrode in the activegroup of electrodes does not exceed the maximum power of the powersupply; and cause each electrode in the active group of electrodes thathas delivered the predefined power for the predefined time duration tobecome inactive.
 10. The computer program product according to claim 9,wherein the plurality of electrodes comprises up to twelve electrodes,and wherein the power supply is configured to provide up to 1.2 kW ofradiofrequency power.
 11. The computer program product according toclaim 9, wherein the catheter comprises a balloon catheter.
 12. Thecomputer program product according to claim 9, wherein the cathetercomprises a basket catheter.